In 1780, Pennsylvania became the first state after the Revolution to abolish slavery by legislative enactment. "An Act for the Gradual Abolition of Slavery" applied to black and mulatto children born after 1780, who would be freed after serving their mothers' masters for 28 years.

Slaveowners were required to register their slaves by November 1, 1780, or they would be automatically emancipated. Domestic slaves of members of Congress, and slaves attending masters who visited Pennsylvania for fewer than six months, were exempt from the registration requirement. Unlike manumission laws in some other states, the Pennsylvania law did not restrict black immigration, nor did it require that freed blacks leave the state.

A year after the law's passage, conservatives attempted to have it repealed. A group of newly-freed blacks quickly petitioned the Pennsylvania Assembly to reject the repeal, concluding by writing, "Fearful of the danger and delay, we have not allowed ourselves time to the collect the names of others with in this city, whose cases are similar to ours; but on the feelings of the honorable house and not on our numbers do we build our hopes."

The petition was reprinted in the September 21, 1781 issue of "Freeman's Journal," along with a letter from Cato, "a poor negro, who with myself and children have had the good fortune to get my freedom." Presumably Cato and his children were free as a result of his master's non-compliance with the registration requirement, since not enough time had elapsed for them to have been manumitted under the law's provisions.

Cato observed that "To make a law to hang us all would be merciful, when compared with this law; for many of our masters would treat us with unheard of barbarity, for daring to take the advantage (as we have done) of the law made in our favor."

He appealed to the lofty principles espoused by the "Christian gentlemen" whose rhetoric informed the original act, writing "I have read the act which made me free, and I always read it with joy." Cato found "particular pleasure" in the passage that declared, "We esteem it a peculiar blessing granted to us, that we are enabled this day to add one more step to universal civilization, by removing, as much as possible, the sorrows of those, who have lived in undeserved bondage."